Additive manufacturing techniques and processes generally involve the buildup of one or more materials, e.g., layering, to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods. Though “additive manufacturing” is an industry standard term (ASTM F2792), additive manufacturing encompasses various manufacturing and prototyping techniques known under a variety of names, including, e.g., freeform fabrication, 3D printing, rapid prototyping/tooling, etc. Additive manufacturing techniques may be used to fabricate simple or complex components from a wide variety of materials. For example, a freestanding object may be fabricated from a computer-aided design (CAD) model.
A particular type of additive manufacturing is commonly known as 3D printing. One such process, commonly referred to as Fused Deposition Modeling (FDM), or Fused Layer Modeling (FLM), comprises melting a thin layer of thermoplastic material and applying this material in layers to produce a final part. This is commonly accomplished by passing a continuous, thin filament of thermoplastic material through a heated nozzle, or by passing thermoplastic material into an extruder, with an attached nozzle, which melts the thermoplastic material and applies it to the structure being printed, building up the structure. The heated material may be applied to the existing structure in layers, melting and fusing with the existing material to produce a solid finished part.
The filament used in the aforementioned process may be produced, for example, by using a plastic extruder. This plastic extruder may be comprised of a steel screw configured to rotate inside of a heated steel barrel. Thermoplastic material in the form of small pellets may be introduced into one end of the rotating screw. Friction from the rotating screw, combined with heat from the barrel, may soften the plastic, which may then be forced under pressure through a small round opening in a die that is attached to the front of the extruder barrel. In doing so, a string of material may be extruded, after which the extruded string of material may be cooled and coiled up for use in a 3D printer or other additive manufacturing system.
Melting a thin filament of material in order to 3D print an item may be a slow process, which may be suitable for producing relatively small items or a limited number of items. The melted filament approach to 3D printing may be too slow to manufacture large items. However, the fundamental process of 3D printing using molten thermoplastic materials may offer advantages for the manufacture of larger parts or a larger number of items.
A common method of additive manufacturing, or 3D printing, may include forming and extruding a bead of flowable material (e.g., molten thermoplastic), applying the bead of material in a strata of layers to form a facsimile of an article, and machining the facsimile to produce an end product. Such a process may be achieved using an extruder mounted on a computer numeric controlled (CNC) machine with controlled motion along at least the x-, y-, and z-axes. In some cases, the flowable material, such as, e.g., molten thermoplastic material, may be infused with a reinforcing material (e.g., strands of fiber or combination of materials) to enhance the material's strength.
The flowable material, while generally hot and pliable, may be deposited upon a substrate (e.g., a mold), pressed down, or otherwise flattened to some extent, and leveled to a consistent thickness, preferably by means of a tangentially compensated roller mechanism. The compression roller may be mounted in or on a rotatable carriage, which may be operable to maintain the roller in an orientation tangential, e.g., perpendicular, to the deposited material (e.g., bead or beads). In some embodiments, the compression roller may be smooth and/or solid. The flattening process may aid in fusing a new layer of the flowable material to the previously deposited layer of the flowable material. The deposition process may be repeated so that successive layers of flowable material are deposited upon an existing layer to build up and manufacture a desired component structure. In some instances, an oscillating plate may be used to flatten the bead of flowable material to a desired thickness; thus, effecting fusion to the previously deposited layer of flowable material. The deposition process may be repeated so that successive layers of flowable material are deposited upon an existing layer to build up and manufacture a desired component structure. When executed properly, the new layer of flowable material may be deposited at a temperature sufficient to allow the new layer of such material to melt and fuse with a previously deposited layer in order to produce a solid part.
In some instances, the process of 3D printing a part may involve a two-step process. For example, the process may utilize a large print bead to achieve an accurate final size and shape. This two-step process, commonly referred to as near-net-shape, may begin by printing a part to a size slightly larger than needed, then machining, milling, or routing the part to the final size and shape. The additional time required to trim the part to a final size may be compensated for by the faster printing process.
In the practice of the aforementioned process, some disadvantages have been encountered. Generally, parts, even relatively large parts, have been printed using relatively small print beads. Because these beads tend to cool quickly, parts are normally printed onto a heated table, and, if a large part is being formed, often the printing process is conducted in a heated environment. This heated environment may slow the rate of cooling of the part as it is being formed via additive manufacturing, keeping newly deposited layers within the desired temperature range for a longer period of time. This longer period of time allows the system to print longer bead lengths for each printed layer without the material cooling below the minimum temperature required to achieve proper layer-to-layer bonding.